1. Field of the Invention
This invention relates generally to the preparation of difurfuryl diamines. In particular, the invention relates to an improved chemical synthesis from biomass of furan-based diamino compounds having the following general formula: ##STR1## where R.sup.1 and R.sup.2 =H, CH.sub.3, CH.sub.3 CH.sub.2, Furan, di-Hydrofuran, and mixtures thereof, or in principle any of a number of other groups or mixture of groups
R.sup.3 =Primarily H, but in principle could consist of CH.sub.3, CH.sub.3 CH.sub.2, or any number of other possible groups or mixture of groups.
2. Description of the Prior Art
Compounds used in the production of polymers have traditionally been synthesized from petroleum-based products. However, declining petroleum reserves, accompanied by the increasing price of petrochemicals, have resulted in a search for alternative sources of chemical feedstocks which are both economical and efficient. It is well known that furan compounds may be generated in almost unlimited quantities from renewable resources, including maize, oat husks, and corn cobs. Other renewable resources, such as hardwoods, also may be potential sources of furan compounds.
The principal utility of the furan compounds produced via the one step method disclosed would be for the production of polymeric compounds. In particular, the compounds would be utilized for adhesives and polyurethane production. The compounds have potential as thermoset adhesives for use with wood composite materials and could also be utilized for the synthesis of condensation polymers from difunctional monomers.
The prior art clearly indicates that to condense carbonyl-containing compounds with furfurylamine, the amino function must be protected during the reaction. The formamide derivative proved to be the most effective. Thus, synthesis of the diamino difurfuryl compounds by the method known to those skilled in the art requires several independent reaction steps including the blocking of the amino group in the original reactant and deblocking of the amino groups to yield the final diamine. This leads to a reaction scheme that is both complex and inefficient.
Cawse et al. [Makromol. Chem. 185:697-707(1984)], in their article titled "Polymers from renewable sources, 1: Diamines and diisocyanates containing difurylalkane moieties," dislose the preparation of furan-based diisocyanates and diamines as potential polymers for polyamide and polyurethane production. The starting materials were methyl furoate and furfurylaine. A one-step reaction scheme was explored in the article. However, this reaction scheme gave only low yields of an undesired Mannich type product together with other products presumed to be homologous oligomers. It is unclear exactly how this reaction was practiced in the prior art since it was not effective and was thus not reported in detail.
Still et al., U.S. Pat. No. 4,496,751, disclose difunctional furan derivatives. To produce the furan derivatives, the amino functionalities are protected by various compounds prior to coupling with the carbonyl compound.
Leon et al, U.S. Pat. No. 2,681,917, disclose a method for the preparation of condensation compounds having two furanic cycles. The method involves reacting a mixture containing substantially two moles of methyl-2-furan and one mole of a reaction component under acid or mineral acid conditions. The reaction component is chosen from the group consisting of aldehydes and ketones having monovalent substituent members. Leon et al is limited to methyl furans which are comparatively easy to condense and are notably different from diamines.